372
Alternative Fuels for Transportation
regenerative braking on all four wheels can significantly improve vehicle
fuel economy.
Figure 12.8 shows a dual-axle complex hybrid system, where the frontwheel axle is propelled by a hybrid drivetrain and the rear-wheel axle is
driven by an electric motor. There are six operating modes. For launching,
the battery delivers electrical energy to feed both the front and rear electric
motors to individually propel the front and rear axles of the vehicle whereas
the engine is in the off mode. For accelerating, both the engine and front
Launching
Cruising
RM
B
E
F
FP
FMG
FT
RT
RP
D
D
RM
B
E
F
FP
FMG
FT
RT
RP
D
D
Accelerating
RM
B
E
F
FP
FMG
FT
RT
RP
D
D
Decelerating/braking
RM
B
E
F
FP
FMG
FT
RT
RP
D
D
Normal driving with battery charging
Axle balancing
B: Battery
E: Engine
F: Fuel tank
D: Differential

FMG: Frontmotor/generator
RM: Rearmotor

FP: Front power converter
RP: Rear power converter

FT: Front axle transmission
RT: Rear axle transmission

RM
B
E
F
FP
FMG
FT
RT
RP
D
D
RM
B
E
F
FP
FMG
FT
RT
RP
D
D
Electrical link
Hydraulic link
Mechanical link
Figure 12.8
Dual-axle (front-hybrid rear-electric) complex hybrid operating modes.